Antibody fragment-targeted immunoliposomes for systemic gene delivery

ABSTRACT

A targeted vector allowing enhanced gene transfer to human hepato-cellular carcinoma (HCC 1 ) cells in vitro was developed using cationic liposomes covalently conjugated with the mAb AF-20. This high affinity antibody recognizes a rapidly internalized 180 kDa cell surface glycoprotein which is abundantly expressed on the surface of human HCC and other cancer cells. Quantitative binding analysis of liposomes with target cells by flow cytometry showed specific association of mAb-targeted liposomes with human HCC cells. Using mAb-targeted cationic liposomes containing 20% DOTAP, in the presence or absence of serum, gene expression in HuH-7 cells was enhanced up to 40-fold as compared to liposomes conjugated with an isotype-matched non-relevant control antibody. Transfection specificity was not observed in a control cell line that does not express the antigen recognized by mAb AF-20. This study demonstrates that cationic liposome foormulations can be targeted with monclonal antibodies (mAbs) to enhance specific in vitro gene delivery and expression in the presence or absence of serum.

BACKGROUND OF THE INVENTION

This invention provides methods for the preparation of antibodyfragment-targeted liposomes (“immunoliposomes”), including lipid-taggedantibody fragment-targeted liposomes, methods for in vitro transfectionusing the immunoliposomes, and methods for systemic gene delivery invivo. The liposomes of the present invention are useful for carrying outtargeted gene delivery and efficient gene expression after systemicadministration. The specificity of the delivery system is derived fromthe targeting antibody fragments.

An ideal therapeutic for cancer would be one that selectively targets acellular pathway responsible for the tumor phenotype and which isnontoxic to normal cells. While cancer treatments involving gene therapyhave substantial promise, there are many issues that need to beaddressed before this promise can be realized. Perhaps foremost amongthe issues associated with macromolecular treatments is the efficientdelivery of the therapeutic molecules to the site(s) in the body wherethey are needed. A variety of delivery systems (a.k.a. “vectors”) havebeen tried including viruses and liposomes. The ideal delivery vehiclewould be one that could be systemically (as opposed to locally)administered and which would thereafter selectively target tumor cellswherever they occur in the body.

The infectivity that makes viruses attractive as delivery vectors alsoposes their greatest drawback. Consequently, a significant amount ofattention has been directed towards non-viral vectors for the deliveryof molecular therapeutics. The liposome approach offers a number ofadvantages over viral methodologies for gene delivery. Mostsignificantly, since liposomes are not infectious agents capable ofself-replication, they pose no risk of transmission to otherindividuals. Targeting cancer cells via liposomes can be achieved bymodifying the liposomes so that they selectively deliver their contentsto tumor cells. There now exists a significant knowledge base regardingspecific molecules that reside on the exterior surfaces of certaincancer cells. Such cell surface molecules can be used to targetliposomes to tumor cells, because the molecules that reside upon theexterior of tumor cells differ from those on normal cells.

The publications and other materials used herein to illuminate diebackground of the invention or provide additional details respecting thepractice, are incorporated by reference.

Current somatic gene therapy approaches employ either viral or non-viralvector systems. Many viral vectors allow high gene transfer efficiencybut are deficient in certain areas (Ledley F D, et al. Hum. Gene Ther.(1995) 6:1129-1144). Non-viral gene transfer vectors circumvent some ofthe problems associated with using viral vectors. Progress has been madetoward developing non-viral, pharmaceutical formulations of genes for invivo human therapy, particularly cationic liposome-mediated genetransfer systems (Massing U, et al., Int. J. Clin. Pharmacol. Ther.(1997) 35:87-90). Features of cationic liposomes that make themversatile and attractive for DNA delivery include- simplicity ofpreparation; the ability to complex large amounts of DNA; versatility inuse with any type and size of DNA or RNA; the ability to transfect manydifferent types of cells, including non-dividing cells; and lack ofimmunogenicity or biohazardous activity (Felgner P L, et al., Ann. NYAcad. Sci. (1995) 772:126-139; Lewis J G, et al., Proc. Natl. Acad Sci.USA (1996) 93:3176-3181). More importantly from the perspective of humancancer therapy, cationic liposomes have been proven to be safe andefficient for in vivo gene delivery (Aoki K et al., Cancer Res. (1997)55:3810-3816; Thierry A R, Proc. Natl. Acad. Sci. USA (1997)92:9742-9746). More than thirty clinical trials are now underway usingcationic liposomes for gene therapy (Zhang W et al., Adv. Pharmacology(1997) 32:289-333; RAC Committee Report: Human Gene TherapyProtocols-December 1998), and liposomes for delivery of small moleculetherapeutics (e.g., antifungal and conventional chemotherapeutic agents)are already on the market (Allen T M, et al., Drugs (1997) 54 Suppl4:8-14).

The transfection efficiency of cationic liposomes can be dramaticallyincreased when they bear a ligand recognized by a cell surface receptor.Receptor-mediated endocytosis represents a highly efficientinternalization pathway present in eukaryotic surface (Cristiano R J, etal., Cancer Gene Ther. (1996) 3:49-57, Cheng P W, Hum. Gene Ther. (1996)7:275-282). The presence of a ligand on a liposome facilitates the entryof DNA into cells through initial binding of ligand by its receptor onthe cell surface followed by internalization of the bound complex. Avariety of ligands have been examined for their liposome-targetingability, including transferrin and folate (Lee R J, et al., J. Biol.Chem. (1996) 271:8481-8487). Transferrin receptors (TfR) levels areelevated in various types of cancer cells including prostate cancers,even those prostate cell lines derived from human lymph node and bonemetastases (Keer H N et al., J. Urol. (1990) 143:381-385); Chackal-Roy Met al., J. Clin. Invest. (1989) 84:43-50; Rossi M C, et al., Proc. Natl.Acad. Sci. USA (1992)89:6197-6201; Grayhack J T. et al., J. Urol.(1979)121:295-299). Elevated TfR levels also correlate with theaggressive or proliferative ability of tumor cells (Elliot R L, et al.,Ann. NY Acad Sci. (1993) 698:159-166). Therefore, TfR levels areconsidered to be useful as a prognostic tumor marker, and TfR is apotential target for drug delivery in the therapy of malignant cells(Miyamoto T, et al., Int. J. Oral Maxillofac. Surg. (1994) 23:430-433:,Thorstensen K. et al., Scand. J. Clin. Lab. Invest. Suppl. (1993)215:113-120). In our laboratory, we have prepared transferrin-complexedcationic liposomes with tumor cell transfection efficiencies in SCCHN of60%-70%, as compared to only 5-20% by cationic liposomes without ligand(Xu L. et al., Hum. Gene Ther. (1997) 8:467-475).

In addition to the use of ligands that are recognized by receptors ontumor cells, specific antibodies can also be attached to the liposomesurface (Allen T M et al., (1995) Stealth Liposomes, pp. 233-244)enabling them to be directed to specific tumor surface antigens(including but not limited to receptors) (Allen T M, Biochim. Biophys.Acta (1995) 1237:99-108). These “immunoliposomes,” especially thesterically stabilized immunoliposomes, can deliver therapeutic drugs toa specific target cell population (Allen T M, et al., (1995) StealthLiposomes, pp. 233-244). Park, et al. (Park J W, et al., Proc. Natl.Acad Sci. USA (1995) 92:1327-1331) found that anti-HER-2 monoclonalantibody (Mab) Fab fragments conjugated to liposomes could bindspecifically to HER-2 overexpressing breast cancer cell line SK-BR-3.The immunoliposomes were found to be internalized efficiently byreceptor-mediated endocytosis via the coated pit pathway and alsopossibly by membrane fusion. Moreover, the anchoring of anti-HER-2 Fabfragments enhanced their inhibitory effects. Doxorubicin-loadedanti-HER-2 immunoliposomes also showed significant and specificcytotoxicity against target cells in vitro and in vivo (Park J W, etal., Proc. Natl. Acad. Sci. USA (1995) 92:1327-1331). In addition,Suzuki et al., (Suzuki S, et al., Br. J. Cancer (1997) 76:83-89) used ananti-transferrin receptor monoclonal antibody conjugated immunoliposometo deliver doxorubicin more effectively in human leukemia cells invitro. Huwyler et al. (Huwyler J, et al., Proc. Natl. Acad. Sci. USA(1996) 93:14164-14169) used anti-TfR monoclonal antibody immunoliposometo deliver daunomycin to rat glioma (RT2) cells in vivo. This PEGylatedimmunoliposome resulted in a lower concentration of the drug in normaltissues and organs. These studies demonstrated the utility ofimmunoliposomes for tumor-targeting drug delivery. It should be notedthat the immunoliposome complexes used by Suzuki et al. and Huwyler etal. differ from those of the invention described herein in that they areanionic liposomes and that the methods used by Suzuki et al. and Huwyleret al. are not capable of delivering nucleic acids.

Single-Chain Antibody Fragments

Progress in biotechnology has allowed the derivation of specificrecognition domains from Mab (Poon R Y, (1997) BiotechnologyInternational: International Developments in the Biotechnology Industry,pp. 113-128). The recombination of the variable regions of heavy andlight chains and their integration into a single polypeptide providesthe possibility of employing single-chain antibody derivatives(designated scFv) for targeting purposes. Retroviral vectors engineeredto display scFv directed against carcinoembryonic antigen, HER-2, CD34,melanoma associated antigen and transferrin receptor have been developed(Jiang A, et al., J. Virol. (1998) 72:10148-10156, Konishi H, et al.,Hum. Gene Ther. (1994) 9:235-248:, Martin F, et al., Hum. Gene Ther.(1998) 9:737-746). These scFv directed viruses have been shown totarget, bind to and infect specifically the cell types expressing theparticular antigen. Moreover, at least in the case of thecarcinoembryonic antigen, scFv was shown to have the same cellularspecificity as the parental antibody (Nicholson I C, Mol. Immunol.(1997) 34:1157-1165).

The combination of cationic liposome-gene transfer and immunoliposometechniques appears to be a promising system for targeted gene delivery.

SUMMARY OF THE INVENTION

We constructed a variety of immunoliposomes that are capable oftumor-targeted, systemic delivery of nucleic acids for use in human genetherapy. Based upon the data given in the Examples below theseimmunoliposome-DNA complexes incorporating the TfRscFv are capable ofproducing a much higher level of transfection efficiency than the sameliposome-DNA complex bearing the complete Tf molecule. Therefore, in oneaspect of the invention the immunoliposomes of the invention can be usedto produce a kit for high efficiency transfection of various mammaliancell types that express the transferrin receptor. In one aspect of theinvention, we constructed an scFv protein with a lipid tag such that thelipid is added naturally by the bacterial cell to allow easyincorporation of the scFv into liposomes while also avoiding chemicalreactions which can inactivate the scFv.

The lipid-tagged scFv-immunoliposomes are prepared basically by twomethods: a lipid-film solubilization method and a direct anchoringmethod. The lipid-film solubilization method is modified from thedetergent dialysis method, which was described by Laukkanen M L, et al.,(Laukkanen M L, et al., Biochemistry (1994) 33:11664-11670) and de Kruifet al., (de Kruif et al., FEBS Lett. (1996) 399:232-236) for neutral oranionic liposomes, with the methods of both hereby incorporated byreference. This method is suitable for attaching lipid-tagged scFv tocationic liposomes as well. In the lipid-film solubilization method, thelipids in chloroform are evaporated under reduced pressure to obtain adry lipid film in a glass round-bottom flask. The lipid film is thensolubilized with 0.54%, preferably 1%, n-octyl β-D-glucoside (OG)containing the lipid-modified scFv and vortexed. After dilution withsterile water, the solution is briefly sonicated to clarity.

The second method for attaching lipid-tagged antibodies or antibodyfragments is the direct anchoring method that is specifically useful forattaching the E coli lipoprotein N-terminal 9 amino acids to an scFv(lpp-scFv) or other lipid-modified antibody or fragments and attachingthese to preformed liposomes. For attaching the scFv to preformedliposomes, the lipid-modified scFv in 1% OG is added to preformedliposomes while vortexing, at volume ratios from 1:3 to 1:10. Themixture is vortexed for approximately a further 5-10 minutes to obtain aclear solution of scFv-immunoliposomes. The remaining OG and theuncomplexed scFv can be eliminated by chromatography, although they willnot interfere very much with the subsequent usage. Separationexperiments, i.e., ultrafiltration with Centricon-100 (Amicon),Ficoll-400 floatation (Shen D F, et al., Biochim. Biophys. Acta (1982)689: 31-37), or Sepharose CL-4B (Pharmacia) chromatography, demonstratedthat virtually all the lipid-tagged scFv molecules added have beenattached or anchored to the cationic liposomes. This is an improvementover the much lower attachment rate of lpp-scFv to neutral or anionicliposomes. Therefore, this improvement makes it unnecessary to include afurther purification step to remove the unattached scFv.

Any antibodies, antibody fragments, or other peptide/protein ligandsthat can be modified to have one or more lipid-tags on the surface areuseful in the present invention. Other lipid-modification methodsinclude directly conjugating a lipid chain to an antibody or fragment,as described in Liposome Technology, 2nd Ed., Gregoriadis, G., Ed., CRCPress, Boca Raton, Fla., 1992.

In another aspect of the invention a cysteine was added at theC-terminus of the scFv sequence and the protein was expressed in theinclusion bodies of E. coli, then refolded to produce active scFv. TheC-terminal cysteine provided a free sulfhydryl group to facilitate theconjugation of the scFv to liposomes. There are two strategies which canbe used in the conjugation process. 1) Pre-linking method: The firststep is to conjugate the scFv-SH with the cationic liposome whichcontains a maleimidyl group or other sulfhydryl-reacting group, to makethe scFv-liposome. The nucleic acids are then added to the scFv-liposometo form the scFv-liposome-DNA complex. The pre-linking is designatedsince scFv is linked before DNA complexing. 2) Post-linking method: Thisstrategy is to complex the cationic liposome with nucleic acids first toform a condensed structure. The scFv-SH is then linked onto the surfaceof DNA-liposome complex to produce scFv-liposome-DNA. The post-linkingis designated since scFv is linked after DNA complexing. Thepost-linking strategy ensures that 100% of scFv linked are on thesurface of the complex, accessible to receptor binding. Therefore, thismethod can make a better use of the targeting ligand scFv and a bettercontrolled inside structure of the complex.

The nucleic acid-immunoliposome complexes, regardless of whether theantibody or antibody fragment is lipid tagged or conjugated to theliposome, can be used therapeutically. Preferably the complexes aretargeted to a site of interest, preferably to a cell which is a cancercell, more preferably to a cell expressing a transferrin receptor. Thetargeting agent is the antibody or antibody fragment which preferablybinds to a transferrin receptor. The nucleic acid is the therapeuticagent and is preferably a DNA molecule and more preferably encodes awild type p53 molecule. The nucleic acid-immunoliposome complexes,preferably in a therapeutic composition, can be administeredsystemically, preferably intravenously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 show scFv TfR lipid-tag construction.

FIG. 2 shows a Western blot analysis of scFv-liposome-targeted p53expression in vivo in tumor xenografts with systemic administration.

FIG. 3 shows pCMVp53 and pCMVpRO constructs.

FIG. 4 shows p53-3′Ad construction.

FIG. 5 shows construction of scFvTfR-cysteine with a His tag.

FIG. 6 shows construction of scFvTfR-cysteine without a His tag. FIG. 7shows construction of scFvTfR-cysteine with a cellulose binding domain(CBD) tag and with an S-tag.

FIG. 8 shows a Coomassie Blue stained SDS-polyacrylamide gel of purifiedTfRscFv protein produced by the conjugation method.

FIG. 9 shows a Western blot analysis of conjugation method producedTfRscFv-liposome-targeted p53 expression in vivo in tumor xenograftswith systemic administration.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to immunoliposomes and methods of making andusing these immunoliposomes. A variety of embodiments are disclosedincluding immunoliposomes with different tags and various methods withwhich to attach the scFv to the liposomes. The immunoliposomes mayinclude lipid tags or be linked through a reducing group, which in apreferred embodiment is a free sulfhydryl.

Mutant forms of the tumor suppressor gene p53 have been associated withmore than 50% of human cancers, including 15-50% of breast and 25-70% ofmetastatic prostate cancers. Abnormalities in p53 also correlate withpoor prognosis in various types of malignancies. Therefore, thecapability to systemically deliver and target gene therapy specificallyto tumors to efficiently restore wtp53 function will be an importanttherapeutic modality in cancer treatment. Thus the immunoliposomesproduced by the method of this invention will be useful as an effectivenew cancer therapeutic modality not just for restoration of wtp53function but also as a tumor targeted systemic delivery vehicle forother therapeutic genes.

The invention is illustrated by the following Examples.

EXAMPLE 1 Construction and Expression of Biosynthetically Lipid-TaggedscFv

1. Construction of the Expression Vector for TfRscFv

To construct the expression vector, we used the vector pLP1 whichcontains an amino acid linker sequence between the E. coli lipoproteinsignal peptide (ssLPP) and the scFv cloning site (de Kruif et al., FEBSLett. (1996) 399:232-236). This vector contains both c-myc and His₆ tagsequences that can be used for purification and detection of theexpressed scFv (FIG. 1).

We obtained a plasmid expression vector, pDFH2T-vecOK, which containsthe single chain fragment for the 5E9 (Haynes et al., J. Immunol. (1981)127:347-351) antibody linked to a DNA binding protein, which recognizesthe human transferrin receptor (TfR). This vector also contains thesequence for a DNA binding protein, and there are no unique restrictionenzyme sites flanking the scFv sequence in pDFH2T-vecOK. Therefore, wecloned the VH-linker-Vκ scFv by PCR amplification of the desiredfragment using a 5′ primer (5′ GGCCCATGGAGGTGCAGCTGGTGG 3′ (SEQ IDNO:1)) (RB551) containing an NcoI site and a 3′ primer (RB552) (5′CCGGAATTCGCGGCCGCTTTTATCTCCAGCTTGGTC 3′ (SEQ ID NO:2) containing a NotIsite. The PCR amplification using primers RB551 and RB552 amplified thescFv for TfR from pDFH2T-vecOK from the Met at base 81 to Lys at base821. The pLP1 vector also contains sequences for the E. coli lipoproteinsignal peptide (ssLPP) and the E. coli lipoprotein N-terminal 9 aminoacids (LPP), as described by Laukkanen M L, et al., (Laukkanen M L, etal., Biochemistry (1994) 33:11664-11670) and de Kruif et al (de Kruif etal., FEBS Lett. (1996) 399:232-236). The insertion of these sequenceswill lead to fatty acid acylation of the expressed signal in the E. colihost and its insertion into the bacterial membrane. The vector also hasa non-critical 10 amino acid linker sequence to increase the spacebetween the lipid-tag site and the scFv. Purification of the lipidmodified scFv sequence from the bacterial membrane results in an activemolecule that can be attached or inserted into liposomes.

2. Expression and Purification of the TfRscFv

We transformed E. coli expression host SF110 F′ with the expressionvector constructed above. While the host cell is not critical it ispreferred that it contain expressed lac repressor. A number of cloneswere selected and the one that produces the best yield of scFv waschosen. The lipid-modified scFv (lpp-scFv) was isolated from thebacterial membrane using Triton X-100 as described by de Kruif et al.,(de Kruif et al., FEBS Lett. (1996) 399:232-236). For purification asingle colony was resuspended in 200 μl LB containing 5% glucose and theappropriate antibiotics. The mixture was plated onto two 90 mm LB agarplates containing 5% glucose and the appropriate antibiotics and grownovernight. The next day, the cells were washed from the plates and usedto inoculate a total of 5 liters of LB containing 0.1% glucose and theappropriate antibiotics. The cultures were grown at 25° C., at 200 rpmfor 6 hours until the OD₆₀₀₀ reached 0.5 to 0.7. IPTG was added to afinal concentration of 1 mM and the cultures were further incubatedovernight. The next day, the bacterial cultures were collected bycentrifugation and lysed in 200 ml lysis buffer at room temperature for30 minutes. The sample was sonicated at 28 watts for 5 minutes withcooling on ice. The lysis buffer contains 20 mM HEPES pH 7.4 to 7.9, 0.5M NaCl, 10% glycerol. and 0.1 mM PMSF. The only deviations from thecited protocol include washing and elution of metal affinity columns inbuffer containing 20 mM HEPES pH 7.4 to 7.9, 0.5 M NaCl, 10% glycerol,0.1 mM PMSF. 1% n-octyl β-D-glucoside (OG), and 10% glycerol containing20 and 200 mM imidazole, respectively. The eluted samples of lpp-scFvwere analyzed by SDS-PAGE and Westem Blot using anti-c-myc antibody 9E10which confirmed that the purified scFv showed a band of the size ofabout 30 kDa.

EXAMPLE 2 Preparation of Lipid-Tagged scFv-Immunoliposomes by aLipid-Film Solubilization Method

This example discloses a detailed procedure of lipid-film solubilizationmethod to prepare lipid-tagged scFv-immunoliposomes. 5 μmol lipids(DOTAP/DOPE, 1:1 molar ratio) in chloroform are evaporated under reducedpressure to obtain a dry lipid film in a glass round-bottom flask. Tothe lipid film is added 0.5 ml 1% OG, 20 mM HEPES, 150 mM NaCl, pH 7.4,containing the lipid-modified scFv. This is incubated 10-20 minutes atroom temperature and then vortexed to solubilize the lipid membrane. 2ml sterile water is then added to dilute the scFv-lipid mixture. Thesolution is briefly sonicated to clarity in a bath-type sonicator at 20°C. The scFv-liposome is a clear solution with a limited amount ofdetergent OG left. The OG aid the uncomplexed scFv can be eliminated bychromatography with Sepharose CL-4B or Sephacryl S500, even though theydo not interfere a lot with the subsequent use.

EXAMPLE 3 Preparation of Lipid-Tagged scFv-Immunoliposomes by a DirectAnchoring Method

This example provides a direct anchoring method to prepare lipid-taggedscFv-immunoliposomes. 20 μmol lipids (LipA-H, see below for compositionsand ratios) prepared as dry lipid film in a glass round-bottom flask isadded to 10 ml pure water and sonicated in a bath-type sonicator for10-30 min at room temperature (LipA, B, C) or at 65° C. (LipD, E, G, H,or any composition with Cholesterol (Chol)). The cationic liposomesprepared are clear solutions, their compositions and ratios are asfollows: LipA DOTAP/DOPE 1:1 molar ratio LipB DDAB/DOPE 1:1 molar ratioLipC DDAB/DOPE 1:2 molar ratio LipD DOTAP/Chol 1:1 molar ratio LipEDDAB/Chol 1:1 molar ratio LipG DOTAP/DOPE/Chol 2:1:1 molar ratio LipHDDAB/DOPE/Chol 2:1:1 molar ratio

For attaching the scFv to preformed liposomes, the lipid-modified scFv(lpp-scFv) in 20 mM HEPES, 150 mM NaCl, pH 7.4, containing 1% OG isadded to preformed liposomes while vortexing, at volume ratios from 1:3to 1:10. The mixture is vortexed for a further 1 to 5 min to get a clearsolution of scFv-immunoliposomes. The remaining OG and the uncomplexedscFv can be eliminated by chromatography although they do not interferevery much with the subsequent usage. Separation experiments, i.e.,ultrafiltration with Centricon-100 (Amicon), Ficoll-400 floatation (ShenD F, et al., Biochim Biophys Acta (1982) 689:31-37), or Sepharose CL-4B(Pharmacia) chromatography, demonstrated that virtually all thelipid-tagged scFv added have been attached or anchored to the cationicliposomes. This is in contrast to the much lower attachment rate oflpp-scFv to neutral or anionic liposomes. Therefore, it is unnecessaryto have a further purification step to get rid of the unattached scFv.

EXAMPLE 4 Immunoreactivity of Lipid-Tagged scFv-Immunoliposomes Revealedby ELISA, FACS and Immunofluorescence

This example provides the characterization of the anti-TfRscFv-immunoliposomes with respect to their ability of binding to theTfR(+) cells. The human prostate cancer cell line DU145 and the humansquamous cell carcinoma of head and neck cell line JSQ-3 served as theTfR+ target cells for these studies.

Indirect cellular enzyme-linked immunosorbent assay (ELISA) was employedto determine the immunoreactivity of the lpp-scFv before and afterattachment to liposomes. Confluent JSQ-3 cells in 96-well plates werefixed with 0.5% glutaraldehyde in PBS for 10 min at room temperature.The plate was blocked with 5% fetal bovine serum (FBS) in PBS at 30° C.for 30 min. The lpp-scFv, scFv-immunoliposomes and liposomes were addedto wells in duplicate and incubated at 4° C. overnight. After threePBS-washes, an anti-c-myc monoclonal antibody was added to each well in3% FBS in PBS and incubated at 37° C. for 60 min. After threePBS-washes, HRP-labeled goat-anti-mouse IgG (Sigma) diluted in 3% FBSwas added to each well and incubated for 30 min at 37° C. The plate waswashed three times with PBS and 100 μl substrate 0.4 mg/ml OPD incitrate phosphate buffer (Sigma) was added to each well. Thecolor-development was stopped by adding 100 μl 2 M sulfuric acid to eachwell. The plate was read by an ELISA plate reader (Molecular DevicesCorp.) at 490 nm. Indirect cellular ELISA demonstrated that the anti-TfRscFv retained its immunoreactivity after incorporation into the toliposome complex (Table 1). TABLE 1 Binding of anti-TfR scFv-liposomesto JSQ-3 cells* Lip(A) only 0.142 ± 0.036 scFv-LipA1 1.134 ± 0.038scFv-LipA2 1.386 ± 0.004 lpp-scFv 0.766 ± 0.009*ELISA, OD₄₉₀, Mean ± SDscFv-LipA1: by lipid-film solubilization method.scFv-LipA2: by direct anchoring method.

For FACS analysis, anti-TfR scFv-Lip(A), was incubated at 4° C. withJSQ-3 and DU145 cells, then with FITC-labeled sheep anti-mouse IgG, alsoat 4° C. Incubation of JSQ-3 cells with the scFv-Lip(A) resulted in afluorescence shift identical to that observed with the unattached freeanti-TfR lpp-scFv antibody demonstrating a significant amount of bindingto the target cells. In contrast, the untargeted liposome demonstratedvery low binding to the cells. Similar results were observed withprostate tumor cell line DU145. Here also, the scFv-Lip(A) complexdemonstrated clear, substantial binding to the tumor cells as comparedto the untargeted Lip(A). The FACS data is summarized in Table 2, wherethe fluorescence shift is indicated as the percent of the cellsdisplaying fluorescence above the threshold level (percent of positivecells). In these studies also, the level of binding to the cells,represented by the percent of positive cells, was similar to that of theunattached free scFv further indicating that incorporation into theliposome complex did not inactivate the immunological activity of theanti-TfR lpp-scFv. It should be noted that the liposome preparation usedfor these initial experiments with DU145 was that optimized for JSQ-3cells. Therefore, the binding of the scFv-targeted liposome complex tothe prostate tumor cells can be further enhanced by the use of theliposome complex optimized for this cell type. TABLE 2 FACS Analysis ofTfRscFv-liposome Binding to JSQ-3 and DU145 JSQ-3 DU145 Transfected by %Positive Mean^(a) % Positive Mean^(a) Untransfected 3.46 4.07 2.22 3.40Lip(A) 9.69 6.26 4.51 4.07 scFv-LipA1 86.38 19.8 50.19 12.40 scFv-LipA289.58 21.30 39.52 11.1 Free lpp-scFv 85.09 21.30 78.09 18.40 HB21^(b)99.44 69.80 98.70 64.90^(a)Mean of the relative fluorescence^(b)Parental monoclonal antibody of the anti-TfR scFv

Indirect immunofluorescence staining with scFv-liposome (where Lip(A)had been labeled with rhodamine-DOPE) and FITC-labeled anti-mouse IgGfollowing anti-c-myc antibody, confirmed the binding of thescFv-targeted liposome complex to the JSQ-3 cells. The concurrence ofthe red and green fluorescence in the transfected cells demonstratesthat the anti-TfR scFv (indicated by the FITC-labeled anti-c-mycantibody as green fluorescence) does indeed direct the rhodamine-labeledLip(A) to the cells. Moreover, the high level of cellular binding of thescFv-Lip(A) system is demonstrated by the large percentage of red/greendouble-positive fluorescent cells.

EXAMPLE 5 Optimization of scFv-Immunoliposome Mediated Gene Transfectionof Target Cells In Vitro

We determined the in vitro transfection efficiency of the anti-TfRscFv-Lip(A) complex in JSQ-3 cells using β-galactosidase as the reportergene. In these studies the reporter construct used contained theβ-galactosidase gene under the control of the CMV promoter (pCMVb), thesame promoter used in pCMVp53 (FIG. 3). The level of β-Gal expression inthe transfected cells (correlating with the transfection efficiency) wasassessed by β-Gal enzymatic assay (Xu L, et al., Hum. Gene Ther. (1997)8:467-475). As shown in Table 3, the attachment of the anti-TfR scFv tothe Lip(A) resulted in a doubling of the enzyme activity in thescFv-Lip(A)-pCMVb transfected cells, as compared to the untargetedliposome complex. This level of expression was also found to bevirtually identical to that observed when transferrin itself was used asthe targeting ligand (Tf-Lip(A)-pCMVb). Moreover, this increase in geneexpression was shown to be reporter gene DNA dose dependent. Table 4shows the optimization of scFv-liposome mediated transfection of JSQ-3cells. TABLE 3 Transfection of JSQ-3 Cells by Anti-TfR scFv-liposomes*DNA (μg/well) Lip(A) only Tf-Lip(A) scFV-LipA1 scFv-LipA2 1.0 475 1031997 1221 0.5 601 981 811 854 0.25 266 503 578 471 0.125 130 262 215 236*milliunits/mg protein, β-galactosidase equivalent, β-Gal enzymaticassayscFv-LipA1: by lipid-film solubilization methodscFv-LipA2: by direct anchoring method

TABLE 4 Optimization of scFv-liposome transfection to JSQ-3* DNA/LipLip(A) scFv- scFv- scFv- scFv- sFv- (μg/nmol) only LipA1 LipA2 LipB LipDLipG ⅛ 1.559 2.793 2.642 1.827 0.874 0.648 1/10 1.776 2.846 2.83 2.2681.606 1.283 1/12 1.868 2.772 2.815 2.175 1.257 1.416 1/14 1.451 3.0312.797 2.31 1.78 1.656*β-Gal enzymatic assay, OD₄₀₅scFv-LipA1: by lipid-film solubilization methodscFv-LipA2: by direct anchoring method

EXAMPLE 6 scFv-Immunoliposome Mediated p53 Gene Transfection Target toTumor Cells Causing Sensitization to Chemotherapeutic Agents

1. Anti-TfR scFv Facilitated Liposome-Mediated wtp53 Gene TransfectionIn Vitro

The expression of exogenous wtp53 in JSQ-3 tumor cells transfected withthe anti-TfR scFv-targeted Lip(A)-p53-3!Ad was assessed byco-transfection of an expression plasmid (pBP100) which contains theluciferase reporter gene under the control of a p53 responsive promoter(Chen L, et al., Proc. Natl. Acad. Sci. USA (1998) 95:195-200).Consequently, the higher the level of exogenous wt p53 expression(representing the scFv-Lip(A)-p53-3′Ad transfection efficiency), thehigher the level of luciferase activity. This luciferase enzyme activityis expressed as relative light units (RLU). As was demonstrated abovewith the β-gal reporter gene, the addition of the anti-TfR scFv as thetargeting agent to the Lip(A)-p53-3′Ad complex resulted in a significantincrease in transfection efficiency and wtp53 protein expression (asexpressed by RLU of Luciferase activity) over the untargetedLip(A)-p53-3′Ad complex (Table 5). Once again, the level of p53expression in the scFv-Lip(A)-p53-3′Ad transfected cells was similar tothat observed when transferrin itself was used as the targeting ligand(LipT(A)-p53-3′Ad). Therefore these findings indicate that the anti-TfRsingle-chain antibody strategy is a useful method of targeting thecationic liposome complex, and delivering a biologically active wtp53gene, to tumor cells. TABLE 5 In Vitro p53 Expression Mediated byDifferent Liposomes in JSQ-3 cells Transfected by RLU* Medium +p53-3′Ad + pBP100 158 Lip(A) + p53-3′Ad + pBP100 4073 LipT(A) +p53-3′Ad + pBP100 7566 scFv-Lip(A1) + p53-3′Ad + pBP100 6441*Relative light units per well2. Anti-TfR scFv-Immunoliposome Mediated p53 Gene Restoration sensitizedthe Tumor Cells to the Cytotoxicity of Cisplatin (CDDP).

For the p53-induced apoptosis study, mouse melanoma cell line B16 wastransfected with anti-TfR scFv-immunoliposome complexed with p53-3′Ad(FIG. 4) or pCMVpRo plasmid (FIG. 3) DNA (scFv-Lip(A)-p53 andscFv-Lip(A)-pRo, respectively) at a dose of 5 μg DNA/2×10⁵ cells in 2sets of 6-well plates. For comparison, transferrin-liposome-DNA(LipT-p53 or LipT-pRo) were also transfected at a dose of 5 μg DNA/2×10⁵cells. 24 hours later, CDDP was added to one set of plates to 10 μMfinal concentration. 24 and 48 hours after the drug was added, both theattached and floating cells were collected for apoptosis staining. Thecells were stained with an Annexin V-FITC Kit (Trevigen, Inc.,Gaithersburg, Md.) according to manufacturer's protocol. Annexin V is alipocortin, a naturally occurring blood protein and anti-coagulant. Thestained cells were analyzed on a FACStar cytometer (Becton andDickinson). Table 6 summarizes the results of the apoptosis analysis.TABLE 6 Apoptosis of B16 Cells Induced by Liposomal p53-gene Restorationand CDDP* 24 hours 48 hours Transfected by −CDDP +CDDP −CDDP +CDDPUntransfected 0.22 4.4 6.33 20.11 LipA-p53 15.9 26.7 15.02 26.52scFv-LipA-p53 13.9 38.4 34.94 43.7 scFv-LipA-pRo 8.1 19.9 24.14 37.59Tf-LipA-p53 22.4 29.5 34.47 31.7 Tf-LipA-pRo 14.1 12.6 14.00 25.34*% of apoptotic cells (Annexin V-FITC positive)

Without CDDP there was no increase in the percent of apoptotic cellsinduced at 24 hours by the addition of the scFv ligand as compared tothe amount induced by the liposome complex alone. However, by 48 hours,there is a greater than 2-fold increase in the percent of apoptoticcells by the addition of the targeting scFv to the lipoplex. With CDDPthere is a significant increase in apoptotic cells (approximately1.5-fold) even at 24 hours as compared to the untargeted liposomecomplex. More significantly, this increase in apoptotic cells incombination with CDDP is more pronounced using the scFv to the Tfreceptor as the targeting ligand than using the Tf molecule itself Thisincrease correlates with transfection efficiency.

EXAMPLE 7 scFv-Immunoliposome-Targeted wtp53 Gene Delivery andExpression In Vivo with Systemic Administration

To examine the ability of the anti-TfR scFv containing liposomes todeliver wtp53 specifically to tumor tissue in vivo, scFv-Lip(A)-p53-3′Ad(FIG. 4) or the untargeted Lip(A)-p53-3′Ad (FIG. 4) was injectedintravenously into nude mice bearing JSQ-3 subcutaneous xenografttumors. Two days after injection, the tumors were excised and proteinisolated from liver and skin, as well as the tumor, for Western blotanalysis (Xu L, et al., Hum. Gene Ther. (1997) 8:467-475). Equal amountsof protein (100 μg, as determined by concentration) were loaded in eachlane. As shown in FIG. 2, the tumor from the mouse systemically treatedwith the scFv-Lip(A)-p53-3′Ad complex, labeled scFv-Lip(A)-p53 in FIG.2, displayed a very intense p53 signal as well as the additional lowerband indicative of a high level of expression of the exogenous wtp53,while only the lower expression of the endogenous mouse p53 is evidentin both the skin and the liver. In contrast, as would be expected basedupon our earlier results, a significantly lower level of exogenous p53expression is evident in the tumor isolated from the untargetedLip(A)-p53-3′Ad injected mouse, labeled Lip(A)-p53 in FIG. 2. Therefore,the liposome complex targeted by our new and unique anti-TfR lpp-scFvligand can clearly deliver exogenous genes selectively to the tumor invivo. These results demonstrate the potential of this new way ofefficiently targeting systemically delivered, cationic liposomecomplexes specifically to tumors in vivo.

EXAMPLE 8 Construction and Purification of TfRscFv with a 3′ Cysteinefor Use in the Conjugation Method

In the absence of a lipid tag, another method was devised to attach thepurified TfRscFv protein to the lipoplex. This approach entails theconjugation of the single chain protein to cationic liposomes via areducible group such as a sulfhydryl group. In the preferred embodimenta cysteine residue is added at the 3′ end of the TfRscFv protein.Reduction of this cysteine results in a free sulfhydryl group which iscapable of being conjugated to cationic liposomes, thus targeting thelipoplex to cells expressing the transferrin receptor. While thefollowing examples use cysteine as the reducible group it is obviousthat other similar reducing groups would also work with this method.

1. Construction

A. Construction of an Expression Vector Containing a 3′ Cysteine with aHistidine Tag for Use in the Conjugation Method of Producing TfRscFvImmunoliposomes

As in Example 1, the VH-linker-Vκ scFv for the TfR was obtained fromplasmid expression vector, pDFH2T-vecOK (described in Example 1). Usinga 5′ primer (5′ GGCCCATGGAGGTGC AGCTGGTGG 3′ (SEQ ID NO:3)) for PCRamplification, an NcoI site was introduced into pDFH2T-vecOK. Thenucleotide sequence for the cysteine residue as well as a NotIrestriction site was introduced using a 3′ primer (5′GGCGCGGCCGCGCATTTTATCTCCAGCTTG 3′ (SEQ ID NO:4)). The PCR product wascloned into NcoI and NotI sites of the commercial vector pET26b(+)(Novagen). This vector also contains, 5′ of the NcoI site, the pelBleader signal sequence. The presence of this sequence in the expressionvector allows transport of the protein to the periplasmic space. To aidin purification of the protein, the pET26b(+) vector also contains aHistidine tag sequence 3′ of the NotI site (FIG. 5).

B. Construction of an Expression Vector Containing a 3′ Cysteine withouta Histidine Tag for Use in the Conjugation Method of Producing TfRscFvImmunoliposomes

For human use as a therapeutic delivery vehicle, it is preferable thatthe TfRscFv be produced without the Histidine tag. Therefore, theconstruct described in Example 8, section 1. A, was modified toeliminate this tag in the final protein product. To accomplish this, thesame 5′ primer as described above (in Example 8, section 1. A) was used.However, a different 3′ primer was used. In addition to the nucleotidesequence for the cysteine residue and the NotI restriction site, thisprimer (5′GGCGCGGCCGCTCAGCATTTTATCTCCAGCTTG 3′ (SEQ ID NO:5)),introduced a DNA stop codon adjacent to the cysteine sequence and beforethe NotI site (FIG. 6). Thus, the protein product of this construct willnot contain the His-tag.

C. Construction of an Expression Vector Containing a 3′ Cysteine with a5′ CBD™-Tag for Use in the Conjugation Method of Producing TfRscFvImmunoliposomes

A third alternative construct containing a cysteine residue for linkageto the cationic lipoplex using the conjugation method was also made. Forthis construct (FIG. 7), the same two primers described above in Example8, section 1 B, were used. Thus no His-tag would be present in theprotein product. However, the PCR product of these reactions was clonedinto a different vector, pET37b(+) (Novagen). This vector contains acellulose binding domain tag (CBD™-tag) and an S-tag, both 5′ of theNcoI site in the vector. The CBD-tag sequence encodes a cellulosebinding domain derived from a microbial cellulase. Thus, the presence ofthis tag enables the use of cellulose-based supports for highlyspecific, low cost affinity purification of the protein product. Thepresence of the S-tag present in this construct allows for easydetection of the protein product on Western blots and for easy enzymaticquantitation of protein amounts.

2. Purification of the TfRscFv Containing the Cysteine Residue

The commercially available E. coli expression host BL21(DE3), whichcontains the expressed lac repressor, was transformed with an expressionvector (all three were used individually) described above in Example 8,section 1. A number of clones were selected and the ones that producedthe best yield of TfRscFv were chosen. Purification of the protein fromthe construct described above in Example 8. section 1. A, with thehistidine tag is given in detail as an example, although the same methodis used for purification of the cysteine containing TfRscFv protein fromall three constructs described in Example 8, section 1. The majority ofthe TfRscFv protein (approximately 90%) was found not to be soluble butto be contained within the inclusion bodies. Therefore, the TfRscFvcontaining the cysteine-linker was purified from the inclusion bodies asfollows. A single clone was inoculated into 5-10 ml LB containing 50μg/ml Kanamycin, and grown at 37° C., and 250 rpm to an OD₆₀₀ of 0.5-0.7(4-5 hrs). 30 ml of the mini culture was pelleted, suspended in LBbroth, added to 1 L LB containing 50 μg/ml Kanamycin and incubated at37° C. and 250 rpm, to an OD₆₀₀ of 0.5-0.7 (4-5 hrs). To induceexpression of the TfRscFv protein, IPTG at a final concentration of 1 mMwas added to the culture at this time and incubation continued for anadditional 4 hrs. This time was determined to yield the maximum level ofprotein expression. The bacterial cultures were then collected bycentrifugation and lysed in 100 ml of cold 20 mM Tris-HCl, pH 7.5,containing 100 μg/ml lysozyme, at 30° C. for 15 minutes. The sample wassonicated at 1 0 watts for 5 minutes (in 30 second bursts) with coolingon ice. The inclusion bodies were isolated by centrifugation at 13,000 gfor 15 minutes. The resulting pellet was washed three times in cold 20mM Tris-HCl buffer, pH 7.5. The purity and quantity of the inclusionbodies were determined by SDS-polyacrylamide gel electrophoresis beforesolubilization.

The isolated inclusion bodies were dissolved in 100 mM Tris-HCl, pH 8.0containing 6 M guanidine-HCl and 200 mM NaCl (6 M GuHCl buffer) andcentrifuged at 12,300 g for 15 minutes to remove insoluble debris.2-mercaptoethanol was added to the supernatant to a final concentrationequal to approximately 50 molar fold of the protein concentration andthe mixture incubated with rotation for 1 hour at room temperature. Thepresence of such a high concentration of guanidine-HCl and the reducingagent results in a totally unfolded protein. Refolding of the TfRscFvprotein was accomplished by dialysis at 4° C. against decreasingconcentrations of guanidine-HCl in the absence of 2-mercaptoethanol:Dialysis was performed for 24 hours each against the followingconcentrations of guanidine-HCl in 100 mM Tris-HCl, pH 8.0 and 200 mMNaCl: 6 M, 3 M, 2 M, 1 M and 0.5 M. The last dialysis was against threechanges of just 100 mM Tris-HCl, pH 8.0 and 200 mM NaCl. The fourthdialysis solution (of 1 M guanidine-HCl) also contained 2 mM glutathione(oxidized form) and 500 mM L-arginine. These reagents allow thepartially refolded protein to form the proper disulfide bonds to producethe correct protein conformation. The solution was clarified bycentrifugation at 13000 g to remove aggregates. The sample wasconcentrated approximately 1.5 fold using the Centrplus centrifugalfilter (Amicon) at 3000 g for 90 min. SDS-PAGE showed a single band ofthe solubilized cysteine containing TfRscFv with a molecular weight ofapproximately 28-30 kDa containing only minor contaminants (FIG. 8).

EXAMPLE 9 Preparation of scFv-Liposomes by the Conjugation Method

1. Reduction of scFv

The purified TfRscFv was reduced by DTT to obtain monomer scFv-SH asfollows: To scFv in HBS (10 mM HEPES, 150 mM NaCl, pH 7.4) was added 1 MDTT to a final concentration of 1-50 mM. After rotation at roomtemperature for 5-10 min, the protein was desalted on a 10-DG column(Bio-Rad). The free —SH group was measured by5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB, Ellman's reagent) (G. L.Ellman (1959) Arch. Biochem. Biophys. 82:70-77. P. W. Riddles, R. L.Blakeley, B. Zeruer (1993) Methods Enzymol. 91:49-60) and calculated as—SH/protein molar ratio, or number of free —SH per scFv molecule (Table7). The results indicate that 1-10 mM DTT is appropriate for the scFvreduction. TABLE 7 Reduction of TfRscFv DTT Concentration (mM) -SH/scFvmolar ratio 0 0.15 1 0.45 10 1.94 20 2.26 50 3.032. Liposome Preparation

4-(p-maleimidophenyl)butyrate-DOPE (MPB-DOPE) (Avanti Polar Lipids) isincluded in the seven liposome formulations described in Example 3, to a5-8% molar of total lipids. The MPB-liposomes were prepared the same wayas described in Example 3. Other liposome preparation methods can alsobe used to prepare the cationic liposomes. For example, the ethanolinjection method modified form that described by Campbell M J(Biotechniques June 1995; 18(6):1027-32) was used successfully in thepresent invention. In brief, all lipids were solubilized in ethanol andmixed, injected into vortexing pure water of 50-60° C. with a Hamiltonsyringe. The solution was vortexed for a further 10-15 min. The finalconcentration was 1-2 mM total lipids. The ethanol injection method isfaster, easier and more robust. 1 M HEPES, pH 7.5 (pH 7.0-8.0) was addedto a final concentration of 10-20 mM. Since we have found that themaleimide group is not stable in aqueous solution with pH>7, theliposomes should be prepared in water (pH 5-6.5). The pH can be adjustedto 7.0-8.0 before linking to scFv-SH with 1 M HEPES buffer, pH 7.0-8.0.to facilitate the post-coating reaction.

3. Preparation of scFv-Liposome-DNA Complexes

A. Pre-Linking Method

scFv-SH was added to MPB-liposome at a protein/lipid (w/w) ratio of1/5-1/40, preferably 1/10-1/20. The solution was mixed by gentlerotation for 30 min at room temperature to yield scFv-Lip. The scFv-Lipwas used without purification although it can be purified by SepharoseCL-4B column chromatography. Plasmid DNA was diluted in water and addedto the scFv-Lip at a DNA/lipid (μg/nmol) ratio of 1/6-1/20, preferably1/10-1/14. The solution was mixed well for 5-15 min by inversion severaltimes to produce scFv-Lip-DNA complex. scFv-Lip-DNA was used withoutpurification although it can be purified by Sepharose CL-4B columnchromatography. 80-100% of the scFv was found to be conjugated to theliposome.

B. Post-linking Method

Plasmid DNA was diluted in water and was added to the MPB-liposome at aDNA/lipid (μg/nmol) ratio of 1/6-1/20, preferably 1/10-1/14. Thesolution was mixed well for 5-15 min by inversion several times toproduce an MPB-Lip-DNA complex. scFv-SH was then added to the complex ata protein/lipid (w/w) ratio of 1/5-1/40, preferably 1/10-1/20. Thesolution was mixed by gentle rotation for 30 min at room temperature, toproduce the final scFv-Lip-DNA complex. The scFv-Lip-DNA was usedwithout purification although it can be purified by Sepharose CL-4Bcolumn chromatography. 80-100% of the scFv was found to be conjugated tothe liposome. 4. For intravenous injection, a 50% dextrose solution wasadded to the scFv-Lip-DNA to a final concentration of 5%.

EXAMPLE 10 Immunoreactivity of Cysteine ContainingTfRscFv-Immunoliposomes by the ELISA Assay

This example provides the characterization of theanti-TfRscFv-immunoliposomes produced by the conjugation method of thisinvention with respect to their ability to bind to TfR(+) cells invitro. Human squamous cell carcinoma of head and neck cell line JSQ-3served as the TfR(+) target cells for these studies.

As previously described in Example 4, indirect cellular enzyme-linkedimmunosorbent assay (ELISA) was employed to determine theimmunoreactivity of the TfRscFv before and after conjugation toliposomes. Confluent JSQ-3 cells in 96-well plates were fixed with 0.5%glutaraldehyde in PBS for 10 min at room temperature. The plate wasblocked with 5% fetal bovine serum (FBS) in PBS at 30° C. for 30 min.The cysteine containing TfRscFv alone, this TfRscFv conjugated tocationic liposomes (TfRscFv-immunoliposomes) and untargeted liposomeswere added to wells in triplicate. An anti-transferrin receptormonoclonal antibody (Hb21, obtained from David Fitzgerald, NIH) was usedin one series of wells as a positive control. The plate was incubated at4° C. overnight. The wells were washed three times with PBS, and ananti-His monoclonal antibody (Qiagen) was added to each well (except forthose receiving the antibody positive control) in 3% FBS in PBS andincubated at 37° C. for 60 min. After three PBS washes, HRP-labeledgoat-anti-mouse IgG (Sigma) diluted in 3% FBS was added to each well andincubated for 30 min at 37° C. The plate was washed three times with PBSand 100 μl substrate 0.4 mg/ml OPD in citrate phosphate buffer (Sigma)was added to each well. The color-development was stopped by adding 100μl 2 M sulfuric acid to each well. The plate was read on an ELISA platereader (Molecular Devices Corp.) at 490 nm.

Indirect cellular ELISA clearly demonstrated that the anti-TfR scFvcontaining a C-terminal cysteine maintained its immunoreactivity. TheOD₄₉₀ values increased with increasing amounts of TfRscFv protein,rising from 0.060±0.0035 with 0.6 μg of protein, to 0.100±0.0038 at 1.5μg and 0.132±0.0031 with 3 μg of TfRscFv. Moreover, this TfRscFv proteinappears to have even greater binding activity than the parental Hb21anti-transferrin receptor antibody used as a positive control. The OD₄₉₀for the highest concentration of the Hb21 (100 μl) was approximately 2-4fold less (0.033±0.0086).

The indirect cellular ELISA assay was also performed after the sameTfRscFv protein was incorporated via the conjugation method of theinvention (Example 9) into two different liposome complexes (Lip(A) andLip(B)) to demonstrate the universality of this method with cationicliposomes. Both the pre- and post-linking conjugation methods ofliposome preparation detailed in Example 9 were used. As shown in Table8, the immunoreactivity of the TfRscFv prepared by the conjugationmethod is not lost through complexing to either of the two liposomecompositions. This was true for both pre- and post-linking methods usedto produce the immunoliposome complex. The TfRscFv-targeted lipoplexesalso demonstrated binding to the cells. This binding was significantlyhigher than that of the liposome without the TfRscFv, suggesting thatthis binding is in fact mediated through the attachment of the TfRscFvto the transferrin receptor on the cells. TABLE 8 Binding ofTfRscFv-immunoliposomes Prepared by the Conjugation Method to JSQ-3Cells In Vitro* DNA:Lipid Ratio OD₄₉₀ Lip(B)-DNA 1:10 0.088TfRscFv-Lip(A)-DNA by Pre- 1:10 0.152 ± 0.016 TfRscFv-Lip(A)-DNA by Pre-1:12 0.166 ± 0.009 TfRscFv-Lip(A)-DNA by Post- 1:12 0.168 ± 0.006TfRscFv-Lip(B)-DNA by Pre- 1:12 0.139 ± 0.012 TfRscFv only — 0.235*ELISA, OD₄₉₀, Mean ± SD (triplicate readings except for Lip(B)-DNA)Pre- = Pre-linking Conjugation MethodPost- = Post-linking Conjugation Method

EXAMPLE 11 Conjugated TfRscFv-Immunoliposome Mediated Gene Transfectionof Target Cells In Vitro

We determined the in vitro transfection efficiency of theTfRscFv-liposome complex, prepared by the conjugation method, in cellsusing the plasmid pLuc, which contains the firefly luciferase gene undercontrol of the CMV promoter as the reporter gene. To demonstrate theuniversality of the TfRscFv as a targeting ligand, here also, as inExample 10, two separate liposome compositions (Lip(A) and Lip(B)) wereconjugated to the TfRscFv protein. Human breast cancer cell lineMDA-MB-435 and human squamous cell carcinoma of the head and neck cellline JSQ-3 were used in these studies. The in vitro transfection wasperformed in 24-well plates (Xu L, et al., Atom. Gene Ther. (1999)10:2941-2952). The transfection solutions were added to the cells in thepresence of 10% serum. 24 hr later the cells were washed and lysed tomeasure the luciferase activity and protein concentration. The resultsare expressed as 10³ relative light units (RLU) per μg protein in thelysate, as shown in Tables 9A and 9B. TABLE 9A ConjugatedTfRscFv-immunoliposome Mediated Transfection In Vitro^(#) LuciferaseActivity (×10³ RLU/μg protein) MDA-MB-435 JSQ-3 LipA 106 377 Tf-LipA 284640 scFv-LipA* 560 1160 scFv-LipA** 660 1210 scFv-LipA (1/10)^(@) — 1315scFv-LipA (1/20)^(@) — 751^(#)Mean of duplicates*Containing 5% MPB-DOPE**Containing 7% MPB-DOPE^(@)Ratio of scFv/lipids (w/w)

TABLE 9B In Vitro Transfection Activity of ConjugatedTfRscFv-Immunoliposome-DNA Complexes Prepared for SystemicAdministration Luciferase Activity (×10³ RLU/μg protein) MDA-MB-435JSQ-3 scFv-LipA-pLuc (pre-linking)* 58.4 675 scFv-LipA-pLuc(pre-linking)** 45.6 513 scFv-LipB-pLuc (pre-linking)* 51.4 415scFv-LipA-pLuc (post-linking)* 58.1 856 scFv-LipA-pLuc (post-linking)**45.3 343 scFv-LipB-pLuc (post-linking)* 47.2 237*Containing 5% MPB-DOPE**Containing 7% MPB-DOPE

The results show that the cysteine containing TfRscFv-immunoliposomesprepared by the conjugation method have very high transfection activityin vitro. 3-6 fold higher than the untargeted liposomes and 2-3 foldhigher than the transferrin-targeted liposomes. This was true for bothliposome compositions and both human tumor cell lines. Thus, they stillretain their immunoreactivity and can bind to their target receptor.Based upon Table 9A, the scFv-liposomes can also be used as efficientgene transfection reagents in vitro and are much more efficient thancommercially available cationic liposomes (DOTAP/DOPE and DDAB/DOPE) andtransferrin-liposomes. The TfRscFv-immunoliposomes disclosed in thepresent invention can be used for an efficient in vitro genetransfection kit useful for the transfection of mammalian cells withtransferrin receptors.

The TfRscFv is a smaller molecule than transferrin itself. Thus, theresulting complex is more compact and more easily taken up by the cellsgiving a higher transfection efficiency. These results are alsoadvantageous for the use of the TfRscFv immunoliposome for systemicdelivery for human use. The smaller size allows increased access to thetumor cells through the small capillaries. Most significantly, theTfRscFv is not a human blood product as is the Tf molecule. Therefore,the concerns and technical problems associated with the use oftransferrin itself for human therapy are avoided.

EXAMPLE 12 Conjugated TfRscFv-Immunoliposome Mediated Expression ofWild-Type p53 in a Nude Mouse Xenograft Model Following SystemicDelivery

In this example the ability of the TfRscFv, produced by the conjugationmethod of this invention, to direct a lipoplex carrying the wild-typep53 (wtp53) gene preferentially to tumor cells in vivo after systemicdelivery is demonstrated. To demonstrate the universality of the TfRscFvas a targeting ligand, here also, as in Example 10, two separateliposome compositions (Lip(A) and Lip(B)) were complexed to thecysteine-containing TfRscFv protein by the conjugation method. Only thepre-linking method of conjugation as detailed in Example 9 was used inthis study. 2.5×10⁶ MDA-MB-435 human breast cancer cells weresubcutaneously injected into 4-6 wk old female athymic nude mice.1.1×10⁷DU145 human prostate cancer cells suspended in Matrigel® collagenbasement membrane (Collaborative Biomedical Products) were alsosubcutaneously injected into 4-6 week old female athymic nude mice andtumors were allowed to develop. Animals bearing tumors of between 50-200mm³ were used in the study (1 animal/sample tested). Conjugated TfRscFvimmunoliposomes carrying the wtp53 gene, as well as untargetedLip(B)-p53 and wtp53 naked DNA were intravenously injected into the tailvein of the animals. As an additional control, conjugated TfRscFv-Lip(A)carrying the empty vector in place of the p53 containing vector was alsoinjected into a mouse. As described in Example 7, approximately 60 hourspost-injection, the animals were sacrificed and the tumors, as well asthe liver, were excised. Protein was isolated from the tissues and 100μg of each sample (as determined by protein concentration assay) was runon a 10% polyacrylamide gel for Western blot analysis using an anti-p53monoclonal antibody. In both of these tumor types the endogenous mouseand the exogenous human p53 migrate at the same position. The resultshere mirror those described in Example 7. As shown in FIG. 9, both theDU145 and MDA-MB-435 tumors from the animals intravenously injected withthe TfRscFv-Lip(A)-pCMVp53 lipoplex or the TfRscFv-Lip(B)-pCMVp53lipoplex prepared by the conjugation method displayed a high level ofexpression of exogenous wtp53, as indicated by the intense p53 signaland an additional lower band, with the best expression in the DU145tumors. While it appears that in both tumor types the Lip(A) compositionwas somewhat better than the Lip(B), both liposome compositions workeddemonstrating the universality of this method. Only the endogenous mousep53 protein was evident in the liver of these animals. In contrast, onlythe endogenous mouse p53 protein was evident in the tumors excised fromthe mice injected with the conjugated TfRscFv-Lip(B) carrying the emptyvector or the naked wtp53 DNA. A small increase in p53 expression alsowas observed in the DU145 tumor with the untargeted Lip(B)-p53. Thus,the conjugated TfRscFv-immunoliposomes delivered the wtp53 genepreferentially to the tumors, as desired. It is also significant thatthis tumor targeting was evident in two different tumor types,indicating the general usefulness of the method of this invention.Therefore, the methods of this invention described in the precedingExamples generate a TfRscFv protein that not only retains its ability tobind to cationic liposomes but is still immunologically activepreserving its ability to bind to the transferrin receptor in vitro andin vivo, thus fulfilling our objective of producing a tumor-specific,targeted immunoliposome for gene therapy.

While the invention has been disclosed in this patent application byreference to the details of preferred embodiments of the invention, itis to be understood that the disclosure is intended in an illustrativerather than in a limiting sense, as it is contemplated thatmodifications will readily occur to those skilled in the art, within thespirit of the invention and the scope of the appended claims.

1-68. (canceled)
 69. A construct for enhanced gene expression inmammalian cells, comprising, from 5′ to 3′: (a) at least one humanadenovirus enhancer sequence; (b) a cytomegalovirus (CMV) promoter; (c)a multiple cloning site; (d) a nucleic acid; and (e) an SV40 poly Asequence; wherein the 3′ end of the plasmid is truncated when comparedto a wild type cytomegalovirus plasmid.
 70. The construct of claim 69,wherein said at least one human adenovirus enhancer sequence comprisestwo instances of Element I and a single instance of Element II.
 71. Theconstruct of claim 69, wherein said mammalian cells are human cells. 72.The construct of claim 69, further comprising a gene conferringantibiotic resistance to said mammalian cells.
 73. The construct ofclaim 72, wherein said antibiotic is kanamycin.
 74. The construct ofclaim 69, wherein said nucleic acid is wild type p53.
 75. A liposomecomplex comprising (i) a liposome, (ii) a cell-targeting ligand, and(iii) the construct of claim
 69. 76. The liposome complex of claim 75,wherein said cell-targeting ligand is an antibody or antibody fragment.77. The liposome complex of claim 76, wherein said antibody fragment isa single chain.
 78. The liposome complex of claim 76, wherein saidantibody or antibody fragment comprises a lipid tag or terminal cysteinemolecule.
 79. The liposome complex of claim 76, wherein said antibody orantibody fragment binds a transferrin receptor.
 80. A method ofexpressing a gene in a mammalian cell, comprising contacting theliposome complex of claim 75 with a mammalian cell under conditionssuitable for transfection and gene expression.
 81. The method of claim80, wherein said mammalian cell is a human cell.
 82. The method of claim80, wherein said contacting comprises administering the liposome complexto a mammal.
 83. The method of claim 82, wherein said administeringcomprises systemically administering.
 84. The method of claim 83,wherein said systemically administering comprises intravenous injection.85. A therapeutic method for the treatment or amelioration of disease ina mammal in need thereof comprising administering to said mammal theconstruct of claim
 69. 86. The therapeutic method of claim 85, whereinsaid nucleic acid in said construct is a therapeutic nucleic acid. 87.The therapeutic method of claim 85, wherein said disease is cancer. 88.A therapeutic method for the treatment or amelioration of disease in amammal in need thereof comprising administering to said mammal aliposome complex comprising a cell targeting ligand, a lipid and theconstruct of claim
 69. 89. The therapeutic method of claim 88, whereinsaid nucleic acid in said construct is a therapeutic nucleic acid. 90.The therapeutic method of claim 88, wherein said cell-targeting ligandis folate, transferrin, an antibody or antibody fragment.
 91. Thetherapeutic method of claim 88, wherein said antibody fragment is asingle chain.
 92. The therapeutic method of claim 88, wherein saidadministering comprises systemic administration.
 93. The therapeuticmethod of claim 88, wherein said disease is cancer.
 94. The therapeuticmethod of claim 93, wherein said complex is intravenously administeredto a cancer-bearing mammal.
 95. The therapeutic method of claim 94,further comprising administering an anti-cancer chemotherapeutic agentor an anti-cancer radiotherapy to said mammal.